I think the inclusion of psionics in D&D were a reflection of the kind of playing around w/genre conventions that was happening in some SF/F during the 70's, with authors importing fantasy conventions into science fiction (like Bradley's Darkover series) and SF conventions into fantasy (like Kurtz's Deryni cycle).
D&D has always been a big ole stew full of nerdery. It's not surprising that 'psionics' (which is always just a science-fictionalizing of old-fashioned mysticism) got thrown into the pot.
D&D has always been a big ole stew full of nerdery. It's not surprising that 'psionics' (which is always just a science-fictionalizing of old-fashioned mysticism) got thrown into the pot.